First make sure you've configured the Fibaro Dimmer 2 correctly, enabling the scene activation functionality – according to the manual, it's parameter 28 set to 1.

That should generate a few new virtual devices, each representing a certain click condition. It can take some trying and reading events to see which device corresponds to which condition (S1 double click, S2 single click, etc). When you've isolated which one means S2 single click, for instance, find the app "If->Then" and create an instance of it. In this configuration you choose the virtual device corresponding to S2 single click in the "If" part, and the scene you want it to activate in the "Then" part.

Then create new instances of the app for the other "click devices" and scenes.

thanks for your reply.
I have enabled the scene activation - but there are no virtual devices generated, whicht I could select.
Do I have to update the database or to do something else to get the virtual devices visible?

Unfortunately, that didn't work out.
I activated parameter #28, triggered the switch S2 (single, double, triple click) and activated the interview between Controller and Dimmer.
But there are still no scene controller visible in the drop down menu of the IF-THEN-App.
Does anybody have a hint for me?

UPDATE: When I activate Scene Activation with my Fibaro Switches, it works - that means, a virtual device is generated which can be used as a condition for IF-THEN.
Nevertheless, it doesn't work at all with my Fibaro Dimmers
Anybody who knows this issue?

Unfortunately, all attempts fail.
While checking the log, I see the scenes are received by Z-Way (e.g. 0x18 for double click) under the command class 43 (scene activation).
Is there an app for listening to certain command classes? Can I trigger a user defined event by listening to a certain command class (in this case: 43)?

With help of the Z-Way support, I've found the solution ... quite simple
The app you need is "Trap events from Remotes and Sensors". By using this app, the events generated by clicking the dimmer S1 or S2 port are autmatically transferred into UI elements which can be easily used for further rule generation!